Conventionally, an industrial electric dust collector is constructed so that dust in a gas is charged by ions formed in corona discharge and is collected on a collecting electrode by the Coulomb force. The collector is mainly composed of a d.c. high-voltage power source, discharge electrode, and collecting electrode, and corona discharge is effected by applying a high voltage of about several tens of kilovolts to the discharge electrode. Before dust is collected, the dust must be moved over the distance to the collecting electrode.
For the electric dust collector, dust is collected by moving dust carrying an electric charge by receiving the Coulomb force in an electric field. The travel velocity is determined by the amount of charge on the dust, electric field strength, air resistance, etc., and in consequence, the particle travel velocity is lowest for fine dust, especially for submicron dust.
The dust collecting efficiency .eta. in the electric dust collector is approximately expressed by .eta.=1-e.sup.-WA/Q (where, W is dust travel velocity, A is area of collecting electrode, and Q is the amound of gas). Therefore, the only means for collecting submicron particles with a low travel velocity with high efficiency is to increase the area of the collecting electrode, which requires a large apparatus, resulting in high cost.
The problem is that dust with a low travel velocity must be moved over a long distance which corresponds to the space between the electrodes and which is several centimeters on average. On the other hand, if dust can be somehow collected with high efficiency even in the case of short travel distances, the efficient collection of submicron particles becomes possible with a small-sized apparatus.
A possible solution to the above problem is a reduction of the space between the discharge and collecting electrodes or narrow spacing. In this case, however, because the contamination of electrodes greatly affect the charging characteristics the performance may even deteriorate, or because the number of electrodes has to be increased, it does not lead to cost reductions.